Description is provided of a conventional coil component with reference to the accompanying drawings. FIG. 16 is a sectional view of a conventional coil component. Coil component 7 comprises first split magnetic core 4 and second split magnetic core 5, each having outer core legs 1, inner core leg 2 and back yoke 3 connecting outer core legs 1 and inner core leg 2, wherein first split magnetic core 4 and second split magnetic core 5 are butted against each other with coil block 6 placed on inner core legs 2. FIG. 17 is a sectional view of the conventional coil component in a configuration showing first split magnetic core 4 and second split magnetic core 5 butted against each other.
First split magnetic core 4 and second split magnetic core 5 are produced by pressure forming magnetic powder with a high pressure exceeding 700 MPa to 1,000 MPa in some cases, by using a powder forming die. In the process of pressure forming, outer core legs 1, inner core legs 2 and back yokes 3 are formed nearly uniformly in their densities by applying generally equal pressure in order to ensure the mechanical strength and magnetic property of first split magnetic core 4 and second split magnetic core 5.
In the case of the conventional coil component, it has been necessary to place many constraints on the shape of the forming die including the need to design outer core legs 1 and inner core legs 2 to have generally similar dimensions and sectional areas for the purpose of forming the individual sections with generally the same pressure when consideration is given to avoid the forming die from being damaged or buckled and to keep its durability and usable life. Patent Literature 1 below, for instance, is one of the technical literatures of the prior art known to be relevant.
According to the intrinsic concept of magnetic circuit design, however, it is rather appropriate for outer core legs 1 and back yokes 3 to have sectional areas smaller than that of inner core legs 2. This is because the magnetic flux φ generated by an electric current flowing in coil block 6 is divided into two flows (φ1 and φ2) toward outer core legs 1 at both sides from inner core leg 2 through back yoke 3, as shown in FIG. 17.
When attempting to reduce the sectional area of outer core legs 1, for instance by decreasing a thickness of outer core legs 1 in the conventional coil component, it becomes necessary to apply a forming die having a smaller sectional area in certain portions, e.g., thinner portions, as compared with other portions in the process of forming first split magnetic core 4 and second split magnetic core 5.
However, there have been some problems associated with the forming die having thin areas such that it is liable to get damaged, buckled down or worn out severely due to the mechanically weak elements, thereby requiring frequent maintenance and posing a variety of constraints when determining a shape of the forming die.
It thus becomes necessary after all to make outer core legs 1 and inner core leg 2 to have generally the same dimensions and sectional area, as shown in FIG. 16 in order to avoid such constraints imposed on the forming die. This results in outer core legs 1 to have a useless volume beyond what is needed, thereby giving rise to a problem that it becomes a factor of impeding downsizing of first split magnetic core 4 and second split magnetic core 5, or coil component 7.